The Atom

1

• The Atom
• Atomic Number and Mass Number
• Isotopes

2
Atoms, Elements, Subatomic Particles

• Atoms The basic unit of a chemical element.
• Elements each of more than one hundred
  substances that cannot be chemically
  inter-converted or broken down into simpler
  substances and are primary constituents of
  matter.
• Subatomic Particles A particle smaller than an
  atom.

3
Atomic Theory

• Atoms are building blocks of elements
• Similar atoms in each element
• Different from atoms of other elements
• Two or more different atoms bond in simple ratios
  to form compounds

4
Subatomic Particles

• Particle Symbol Charge Relative
• Mass
• Electron e- 1- 0
• Proton p 1
• Neutron n 0 1

5
Location of Subatomic Particles

• 10-13 cm
• electrons
• protons
• neutrons
• 10-8 cm

nucleus
6
Atomic Number

• Counts the number
• of
• protons
• in an atom

7
Periodic Table

• Represents physical and chemical behavior of
  elements
• Arranges elements by increasing atomic number
• Repeats similar properties in columns known as
  chemical families or groups

8
Periodic Table

• 1 2 3 4 5 6 7 8

11 Na
9
Atomic Number on the Periodic Table

• 11
• Na

Atomic Number
Symbol
10
All atoms of an element have the same number of
protons

• 11
• Na

11 protons
Sodium
11
Learning Check AT 1

• State the number of protons for atoms of each
  of the following
• A. Nitrogen
• 1) 5 protons 2) 7 protons 3) 14
  protons
• B. Sulfur
• 1) 32 protons 2) 16 protons 3) 6
  protons
• C. Barium
• 1) 137 protons 2) 81 protons 3) 56
  protons

12
Solution AT 1

• State the number of protons for atoms of each of
  the following
• A. Nitrogen
• 2) 7 protons
• B. Sulfur
• 2) 16 protons
• C. Barium
• 3) 56 protons

13
Number of Electrons

• An atom is neutral
• The net charge is zero
• Number of protons Number of electrons
• Atomic number Number of electrons

14
Mass Number

• Counts the number
• of
• protons and neutrons
• in an atom

15
Atomic Symbols

• Show the mass number and atomic number
• Give the symbol of the element
• mass number
• 23 Na sodium-23
• atomic number 11

16
More Atomic Symbols

• 16 31 65
• O P Zn
• 8 15 30
• 8 p 15 p 30 p
• 8 n 16 n 35 n
• 8 e- 15 e- 30 e-

17
Isotopes

• Atoms with the same number of protons, but
  different numbers of neutrons.
• Atoms of the same element (same atomic number)
  with different mass numbers
• Isotopes of chlorine
• 35Cl 37Cl
• 17 17
• chlorine - 35 chlorine - 37

18
Learning Check AT 2

• Naturally occurring carbon consists of three
  isotopes, 12C, 13C, and 14C. State the number of
  protons, neutrons, and electrons in each of these
  carbon atoms.
• 12C 13C 14C
• 6 6
  6
• P _______ _______
  _______
• N _______ _______
  _______
• E _______ _______
  _______

19
Solution AT 2

• 12C 13C 14C
• 6 6
  6
• P __6___ _ 6___
  ___6___
• N __6___ _ _7___
  ___8___
• E __6___ _ 6___
  ___6___

20
Learning Check AT 3

• An atom of zinc has a mass number of 65.
• A. Number of protons in the zinc atom
• 1) 30 2) 35 3) 65
• B. Number of neutrons in the zinc atom
• 1) 30 2) 35 3) 65
• C. What is the mass number of a zinc isotope
• with 37 neutrons?
• 1) 37 2) 65 3) 67

21
Solution AT 3

• An atom of zinc has a mass number of 65.
• A. Number of protons in the zinc atom
• 1) 30
• B. Number of neutrons in the zinc atom
• 2) 35
• C. What is the mass number of a zinc isotope
• with 37 neutrons?
• 3) 67

22
Learning Check AT 4

• Write the atomic symbols for atoms with the
  following
• A. 8 p, 8 n, 8 e- ___________
• B. 17p, 20n, 17e- ___________
• C. 47p, 60 n, 47 e- ___________

23
Solution AT 4

• 16O
• A. 8 p, 8 n, 8 e- 8
• B. 17p, 20n, 17e- 37Cl
• 17
• C. 47p, 60 n, 47 e- 107Ag
• 47

24
Learning Check AT 5

• An atom has 14 protons and 20 neutrons.
• A. Its atomic number is
• 1) 14 2) 16 3) 34
• B. Its mass number is
• 1) 14 2) 16 3) 34
• C. The element is
• 1) Si 2) Ca 3) Se
• D. Another isotope of this element is
• 1) 34X 2) 34X 3) 36X
• 16 14
  14

25
Solution AT 5

• An atom has 14 protons and 20 neutrons.
• A. It has atomic number
• 1) 14
• B. It has a mass number of
• 3) 34
• C. The element is
• 1) Si
• D. Another isotope of this element would be
• 3) 36X
• 14

26
Masses of Atoms

• A scale designed for atoms gives their small
  atomic masses in atomic mass units (amu)
• An atom of 12C was assigned an exact mass of
  12.00 amu
• Relative masses of all other atoms was
  determined by comparing each to the mass of 12C
• An atom twice as heavy has a mass of 24.00 amu.
  An atom half as heavy is 6.00 amu.

27
Atomic Mass
Na 22.99

• Listed on the periodic table
• Gives the mass of average atom of each element
  compared to 12C
• Average atom based on all the isotopes and their
  abundance
• Atomic mass is not a whole number

28
Learning Check AT6

• Using the periodic table, specify the atomic
  mass of each element (round to the tenths place)
  
• A. calcium __________
• B. aluminum __________
• C. lead __________
• D. barium __________
• E. iron __________

29
Solution AT6

• Using the periodic table, specify the atomic
  mass of each element (round to the tenths place)
• A. calcium _40.1 amu _
• B. aluminum _27.0 amu _
• C. lead _207.2 amu_
• D. barium _137.3 amu_
• E. iron _55.8 amu__

30
Calculating Atomic Mass

• Percent() abundance of isotopes
• Mass of each isotope of that element
• Weighted average
• mass isotope1() mass isotope2()
• 100 100

31
Atomic Mass of Magnesium

• Isotopes Mass of Isotope Abundance
• 24Mg 24.0 amu 78.70
• 25Mg 25.0 amu 10.13
• 26Mg 26.0 amu 11.17
• Atomic mass (average mass) Mg 24.3 amu

Mg 24.3
32
Learning Check AT7

• Gallium is a metallic element found in small
  lasers used in compact disc players. In a sample
  of gallium, there is 60.2 of gallium-69 (68.9
  amu) atoms and 39.8 of gallium-71 (70.9 amu)
  atoms. What is the atomic mass of gallium?

33
Solution AT7

• Ga-69
• 68.9 amu x 60.2 41.5 amu for 69Ga
• 100
• Ga-71 (/100)
• 70.9 amu x 39.8 28.2 amu for 71Ga
• 100
• Atomic mass Ga 69.7 amu

34
Finding An Isotopic Mass

• A sample of boron consists of 10B (mass 10.0
  amu) and 11B (mass 11.0 amu). If the average
  atomic mass of B is 10.8 amu, what is the
  abundance of each boron isotope?

35

• Assign X and Y values
• X 10B Y 11B
• Determine Y in terms of X
• X Y 100
• Y 100 - X
• Solve for X
• X (10.0) (100 - X )(11.0) 10.8
• 100 100
• Multiply through by 100
• 10.0 X 1100 - 11.0X 1080

36

• Collect X terms
• 10.0 X - 11.0 X 1080 - 1100
• - 1.0 X -20
• X -20 20 10B
• - 1.0
• Y 100 - X
• 11B 100 - 20 80 11B

37
Learning Check AT8

• Copper has two isotopes 63Cu (62.9 amu) and 65Cu
  (64.9 amu). What is the abundance of each
  isotope? (Hint Check periodic table for atomic
  mass)
• 1) 30 2) 70 3) 100

38
Solution AT8

• 2) 70
• Solution
• 62.9X 6490 64.9X 6350
• -2.0 X -140
• X 70